<!--Copyright (C) 1988-2005 by the Institute of Global Environment and Society (IGES). See file COPYRIGHT for more information.-->
<html>
<title>GrADS Function: atot</title>
<style type="text/css">
.red {
color: #900;
font-weight: bold;
}
.red1 { color: #900;
}
body {
background-color: #e0f0ff;
}
</style>
<body text="#000000">
<H2><b>atot()</b></H2>
<p>Thie <code>atot</code> function (in <span class="red1">GrADS version 2.0.2+</span>) duplicates the summing capability of <code><a href="gradfuncasum.html">asum</a></code> but adds the latitude-weighting feature of <code><a href="gradfuncaave.html">aave</a></code>. The syntax is:
<p>
<code>atot(<i>expr, xdim1, xdim2, ydim1, ydim2</i>)</code>
<p>
<H3>Usage Notes</H3>
<p>Please see the reference page for <code><a href="gradfuncasum.html">asum</a></code> for details on the command syntax and usage notes.
<br>
<H3>Examples</H3>
<ol>
<li>
<p>An instructive sanity check is to calculate the total area over globe on any grid of data that has a constant value of 1 and no missing values: <br>
<br>
<code>ga-> d atot(const(temp,1,-a),global) <br>
Result value = 12.5664 </code><br>
<br>
The answer we get is 4*pi, and the unit of the result is steradians.
<li>Suppose you have a data variable sea ice concentration (named 'sic') which is given as a % in each grid box, and you would like to calculate the total area in the Arctic covered by sea ice.
To calculate the sea ice coverage in millions of km^2, we multiply the <code>atot</code> result by the square of the radius of the Earth in km:
<p><code>ga-> d atot(sic/100,lon=0,lon=360,lat=40,lat=90)*6371*6371*1e-6 <br>
Result value = 11.289</code>
</ol>
</body>
</html>
